Github action assign a variable of type env an array of strings

Question

I am having the following problem what you see in the image.

I have a.js file which returns me an array of url strings. Then I should assign this array to an env variable as seen in the example below, but I get the following error.

You can tell me where I'm wrong.

on: 
  workflow_dispatch:
  
name: Test Download Multifile
jobs:
  build:
    name: Build
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v2
        name: Check out current commit
     
      - name: Url
        run: |
         URL=$(node ./actionMultifile.js)
         echo $URL
         echo "URL=$URL" >> $GITHUB_ENV

actionMultifile.js

async function getData(){
 const url = [
   "https://upload.wikimedia.org/wikipedia/commons/thumb/c/c9/Tyrannosaurus_rex_Sue_at_FMNH.jpg/440px-Tyrannosaurus_rex_Sue_at_FMNH.jpg",
   "https://upload.wikimedia.org/wikipedia/commons/thumb/b/bc/Mosasaurus_beaugei_34.JPG/440px-Mosasaurus_beaugei_34.JPG"
 ]
 return url;
}

getData().then((url) => {
 console.log(url);
});